The present invention broadly relates to a new and improved construction of a back rest arrangement on a weaving machine.
In its more particular aspects, the present invention relates to a new and improved construction of a back rest arrangement on a weaving machine whose back rest is supported in positionally variable or adjustable manner.
In modern weaving machines it is usual to regulate the rotary drive of the warp beam so as to generate a tension force on the warp thread sheets which is as constant as possible, for which purpose the tension of the warp thread being unwound or let off is employed as the control variable.
Correspondingly, the determination of the tension in the warp threads is effected near the warp beam in the region of the back rest which deflects the warp threads into a horizontal direction towards the weaving shed.
For example, in accordance with the German Patent Publication No. 3,406,888 the back rest is pivotably supported; through spring-loaded bell cranks or angle levers in the manner of a compensating roller and the free ends of the bell cranks or angle levers cooperate with a proximity switch which delivers an electrical signal which is proportional to the tension of the warp thread sheets.
As can, for instance, be seen from French Utility or Petty Patent No. 8,019,224, other embodiments are known which utilize additional compensating rollers.
All these known arrangements are relatively complicated. Furthermore they cannot be easily utilized in weaving machines where the back rest is supported by a so-called rocking lever or rocker beam. The back rest is supported at such rocker beam for the purpose of being able to adjust the position of the back rest, by suitable adjustment means, in addition to the positional change caused by the varying warp thread tension. Such adjustment is necessary in order to generate additional warp thread tension when starting operation of the weaving machine. This can be particularly well seen from German Patent No. 2,927,533.